Module 6 - 4 Flashcards
(22 cards)
What are serine proteases?
Enzymes that cleave peptide bonds in proteins.
What is the function of zymogens?
To prevent damage to cellular proteins.
How are zymogens activated?
By selective proteolysis.
What is the catalytic mechanism of serine proteases?
Contains elements of both covalent and acid-base catalysis.
What is the substrate specificity of thrombin?
Cleaves Arg-Gly bonds.
What is the substrate specificity of trypsin?
Cleaves by Lys and Arg.
What is the substrate specificity of chymotrypsin?
Cleaves by Phe, Tyr or Met.
What is the substrate specificity of elastase?
Cleaves by Gly and Ala.
What is the substrate specificity of papain?
Cuts all peptide bonds.
What is the catalytic triad of serine proteases?
A conserved mechanism based on Asp, His, Ser residues.
What is the role of His in the catalytic triad?
Accepts and donates a proton in acid-base catalysis.
What is the role of Asp in the catalytic triad?
Stabilizes the positively-charged His.
What is the role of Ser in the catalytic triad?
Attacks the carbonyl group of the peptide bond.
What is the overview of the chymotrypsin mechanism?
Two-phase mechanism involving acid-base and covalent catalysis.
What happens in Phase I of the chymotrypsin mechanism?
Histidine acts as a base to activate the oxygen of the hydroxyl group of Ser.
What happens in Step 2 of Phase I of the chymotrypsin mechanism?
Formation of a covalent linkage between Ser and the carbonyl carbon of the peptide bond.
What happens in Step 3 of Phase I of the chymotrypsin mechanism?
Histidine acts as an acid to cut the substrate peptide into two pieces.
What happens in Phase II of the chymotrypsin mechanism?
Histidine acts as a base to activate a water molecule.
What is Step 2 in enzyme catalysis?
Activated water molecule attacks covalent linkage.
What is Step 3 in enzyme catalysis?
Histidine acts as an acid to donate a proton.
What type of water molecule is involved in Step 2?
Covalently activated water molecule.
What is the role of histidine in Step 3?
Acts as an acid to donate a proton.
